title: Contribution of hydrophobic interactions to protein stability.
abstract: Our goal was to gain a better understanding of the contribution of hydrophobic interactions to protein stability. We measured the change in conformational stability, Δ(ΔG), for hydrophobic mutants of four proteins: villin headpiece subdomain (VHP) with 36 residues, a surface protein from Borrelia burgdorferi (VlsE) with 341 residues, and two proteins previously studied in our laboratory, ribonucleases Sa and T1. We compared our results with those of previous studies and reached the following conclusions: (1) Hydrophobic interactions contribute less to the stability of a small protein, VHP (0.6±0.3 kcal/mol per -CH(2)- group), than to the stability of a large protein, VlsE (1.6±0.3 kcal/mol per -CH(2)- group). (2) Hydrophobic interactions make the major contribution to the stability of VHP (40 kcal/mol) and the major contributors are (in kilocalories per mole) Phe18 (3.9), Met13 (3.1), Phe7 (2.9), Phe11 (2.7), and Leu21 (2.7). (3) Based on the Δ(ΔG) values for 148 hydrophobic mutants in 13 proteins, burying a -CH(2)- group on folding contributes, on average, 1.1±0.5 kcal/mol to protein stability. (4) The experimental Δ(ΔG) values for aliphatic side chains (Ala, Val, Ile, and Leu) are in good agreement with their ΔG(tr) values from water to cyclohexane. (5) For 22 proteins with 36 to 534 residues, hydrophobic interactions contribute 60±4% and hydrogen bonds contribute 40±4% to protein stability. (6) Conformational entropy contributes about 2.4 kcal/mol per residue to protein instability. The globular conformation of proteins is stabilized predominantly by hydrophobic interactions.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA. nickpace@tamu.edu
authors.forename: C Nick
authors.initials: CN
authors.lastname: Pace
authors.forename: Hailong
authors.initials: H
authors.lastname: Fu
authors.forename: Katrina Lee
authors.initials: KL
authors.lastname: Fryar
authors.forename: John
authors.initials: J
authors.lastname: Landua
authors.forename: Saul R
authors.initials: SR
authors.lastname: Trevino
authors.forename: Bret A
authors.initials: BA
authors.lastname: Shirley
authors.forename: Marsha McNutt
authors.initials: MM
authors.lastname: Hendricks
authors.forename: Satoshi
authors.initials: S
authors.lastname: Iimura
authors.forename: Ketan
authors.initials: K
authors.lastname: Gajiwala
authors.forename: J Martin
authors.initials: JM
authors.lastname: Scholtz
authors.forename: Gerald R
authors.initials: GR
authors.lastname: Grimsley
mesh_terms: D000942:Antigens, Bacterial / Q000737:chemistry* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D019277:Entropy; D057927:Hydrophobic and Hydrophilic Interactions; D008074:Lipoproteins / Q000737:chemistry* / Q000235:genetics; D008840:Microfilament Proteins / Q000737:chemistry* / Q000235:genetics; D009154:Mutation; D011487:Protein Conformation; D055550:Protein Stability; D006163:Ribonuclease T1 / Q000737:chemistry* / Q000235:genetics; D012260:Ribonucleases / Q000737:chemistry* / Q000235:genetics
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D008074:Lipoproteins; D008840:Microfilament Proteins; C105546:VlsE protein, Borrelia burgdorferi; C026615:villin; D012260:Ribonucleases; C077002:ribonuclease Sa3; D006163:Ribonuclease T1